3D printing of a composite material via sequential dual-curing polymerization

ABSTRACT

A method of printing a 3D printing a photopolymer composite material includes providing a resin premix material including an acrylate monomer or an acrylate oligomer, an inorganic hydrate, a reinforcing filler, a co-initiator, and an ultraviolet (UV) initiator. A thermal initiator is mixed with the resin premix to form a photopolymer composite resin. The photopolymer composite resin is repeatedly extruded and dual-cured by a 3D printing system to create a photopolymer composite material. The 3D printing system includes a control system, a mixing system, a feeding system in fluid communication with the mixing system, a light curing module controlled by the control system, and a printing head controlled by the control system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/541,081, filed on Aug. 14, 2019, which is hereby incorporated byreference in its entirety.

BACKGROUND

Three-dimensional (3D) printing, also known as additive manufacturing,is a technique that deposits materials only where needed, thus resultingin significantly less material wastage than traditional manufacturingtechniques, which typically form parts by reducing or removing materialfrom a bulk material. While the 3D printed articles were generallymodels, the industry is quickly advancing by creating 3D printedarticles that may be functional parts in more complex systems, such ashinges, tools, structural elements.

In existing 3D printing processes, a 3D object is created by forminglayers of material under computer control without molding. For example,3D information of a structure is determined using computer 3D modelingfragmentation and a prepared mixture can be fed from a nozzle bymechanical control to print the structure.

One serious problem and challenge of 3D printing is that printingmaterials meeting requirements of certain applications can be veryscarce. For example, existing printing materials are mainly organicmaterials. The organic materials are printed in a molten state at a hightemperature via layer by layer deposition. Curing of the organicmaterials is prone to oxidation decomposition, and the preparation andprinting processes may emit unpleasant toxic gases that harm theenvironment and human health. In addition, the organic materials may beprinted under demanding conditions which incur high costs. Structuresprinted with the organic materials may have poor mechanical propertiesand are therefore not suitable for certain applications such asconstructing livable buildings, thus limiting the application of 3Dprinting technology to a certain extent.

Another example of printing material is cement-based materials such asconcrete. Cement-based materials generally take a long time to solidify.Thus, such materials generally cannot meet performance requirementsrequiring the material to rapidly solidify in a short period of time.Even though the speed of solidification can be increased by changing theformulation, such increase is usually limited or difficult to controland makes 3D printing impractical for certain circumstances such asconstructing a building on a construction site.

In view of the foregoing, there is a need for improvements and/oralternative or additional solutions to improve 3D printing materials andprocesses.

In conventional additive or three-dimensional fabrication techniques,construction of a three-dimensional object is performed in a stepwise orlayer-by-layer manner. In particular, layer formation is performedthrough solidification of photo curable resin under the action ofvisible or UV light irradiation. Two techniques are known: one in whichnew layers are formed at the top surface of the growing object; theother in which new layers are formed at the bottom surface of thegrowing object. Photochemical curing, also known as photopolymerization,is an inexpensive and efficient method of additive manufacturing.

The main drawback of light-curing is the limited penetration of lightradiation into the irradiated material, which gets even more limited inpresence of colored, semi-transparent, or opaque additives, which arefrequently used to give the material functional properties. In any knownlayer-by-layer printing process using polymer materials, the polymermatrix embedded with the composition of the filler must allow UV lightpenetration depth to be sufficient for a complete layer solidification.

The other issue related to photopolymerization is that non-uniformvolume shrinkage occurs upon polymerization, which results in a highlevel of residual stress and detrimental warpage or curvature of theprinted samples. The bulk volume shrinkage in photopolymerization is anunavoidable result of the formation of new covalent bonds via the vander Waals force. As a result, polymerization strains are introducedincrementally, layer-by-layer during 3D printing, thereby giving rise toresidual stresses. If the stress exceeds the adhesive strength of anycomponent of the system, micro- or macro-deformations occur (cracking,delamination, etc.) during and after printing.

Retailleau, Ibrahim and Allonas, Polymer Chemistry 5, 6503 (2014),describe UV-curing polymerization of acrylates assisted by a thermalpolymerization, but the proposed system requires a significant time tocure at the surface. Thus, it does not fit for additive manufacturing,especially for extrusion-based additive manufacturing, and no suggestionis made on how those materials may be adapted to additive manufacturing.

Rolland, and Menio, patent application WO2017040883A1, describedual-cure cyanate ester resin for additive manufacturing. McCall, patentapplication WO2017112521A1, describes dual-curepolyurethane/polyurea-containing resins for additive manufacturing. Bothabove-mentioned inventions describe combination of layer-by-layerphotopolymerization, preferably DLP or CLIP methods, followed by thermalcuring to form two interpenetrating polymer networks. This mainshortcoming of this method is the need to perform additive manufacturingin two subsequent stages, which increases production time and requiredlabor, and adds additional equipment costs.

Therefore, there is a need to develop a novel composite that will solvethe above-mentioned shortcomings of the existing formulations.

BRIEF SUMMARY

This disclosure relates to a method of 3D printing a photopolymercomposite material, the method comprising first providing a resin premixmaterial including at least one of an acrylate monomer and an acrylateoligomer in the range between about 10.0-30.0 w % of a photopolymercomposite resin, an inorganic hydrate in the range between about5.0-30.0 w % of the photopolymer composite resin, a reinforcing fillerin the range between about 50.0-80.0 w % of the photopolymer compositeresin, an ultraviolet (UV) initiator in the range between about0.001-0.2 w % of the photopolymer composite resin, and a co-initiator inthe range between about 0.001-0.05 w % of the photopolymer compositeresin. The method further comprises mixing a thermal initiator in therange between about 0.001-0.05 w % of the photopolymer composite resinwith the resin premix material to form the photopolymer composite resin.The method next comprises extruding a layer of the photopolymercomposite resin using a 3D printer onto a support and at least partiallycuring the layer using light irradiation. The method finally comprisesrepeating the steps of extrusion and partial curing onto each subsequentlayer to create the photopolymer composite material, which may be a 3Dprinted part.

This disclosure further relates to a 3D printing system comprising acontrol system, a mixing system, a feeding system in fluid communicationwith the mixing system, a light curing module controlled by the controlsystem, and a printing head controlled by the control system. Theprinting head includes a fluid communication with the feeding system, anextruder in fluid communication with the feeding system, a nozzle influid communication with the extruder, and the mixing system supplying aresin premix material generated by the method disclosed herein. Thefeeding system supplies a thermal initiator in the range between about0.001-0.05 w % of the photopolymer composite resin and the resin premixmaterial to form the photopolymer composite resin. The extruder deliversthe photopolymer composite resin to the nozzle. The control systeminstructs the nozzle to extrude a layer of the photopolymer compositeresin onto a support. The control system further instructs the lightcuring module to at least partially cure the layer using lightirradiation. The control system controls the repetition of the extrusionand curing steps onto each subsequent layer to create a photopolymercomposite material, which may be a 3D printed part.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To easily identify the discussion of any particular element or act, themost significant digit or digits in a reference number refer to thefigure number in which that element is first introduced.

FIG. 1 illustrates end material 100 in accordance with one embodiment.

FIG. 2 illustrates end material 200 in accordance with one embodiment.

FIG. 3 illustrates a method 300 in accordance with one embodiment.

FIG. 4 illustrates a mixing system and feeding system 400 in accordancewith one embodiment.

FIG. 5 illustrates a method 500 in accordance with one embodiment.

FIG. 6 illustrates a printing system 600 in accordance with oneembodiment.

FIG. 7 illustrates a control system 700 in accordance with oneembodiment.

FIG. 8 illustrates a curing comparison 800 in accordance with oneembodiment.

FIG. 9 illustrates a curing process detail 900 in accordance with oneembodiment.

FIG. 10 illustrates layers with carbon dust 1000 in accordance with oneembodiment.

FIG. 11 illustrates cellular structure concepts 1100 in accordance withone embodiment.

DETAILED DESCRIPTION

The present invention is related to a new composition that comprises ofpolymer matrix, inorganic fillers and a complex of polymerizationinitiating agents, providing a stable single-stage 3D printing process.In some embodiments, the invented composition may include a flexiblevariation of the printing speed and embed into the polymer matrix themineral fillers of different nature, including semi-transparent, opaque,and colored particles.

To resolve the existing issues, the dual-cure process may be implementedby using the co-initiation system, including the use of photoinitiators, thermal initiators and others. The synergistic effects ofmultiple initiation agents have been explored and described. Theapplication of a dual-cure (i.e., dual-initiation) system opensopportunities for the on-demand curing of polymer materials. A compositematerial may combine properties of a polymer matrix and microcrystallineinorganic fillers. The material may comprise a base acrylate monomerand/or acrylate oligomer, filler composition, and a system ofco-initiating agents of photo- and thermal-polymerization, which mayinduce a dual-cure reaction of the monomer/oligomer ensure a stableprinting process.

A photopolymer composite material combines properties of a polymermatrix and microcrystalline inorganic fillers. The material comprises abase acrylate monomer, filler composition and system of co-initiatingagents of photo and thermal-polymerization which induce dual-curereaction of the monomer, ensuring stable printing process. With thelayer-by-layer deposition of the material in the 3D printing process,each newly deposited layer may undergo consistent photo- andthermal-polymerization curing. Properties of photopolymer compositeresin may depend on the quantity of the components utilized in theformulation. When uncured, the material may be a thixotropic liquid. Thematerial may be transported through the feeding route by pumps and thenextruded. When exposed to UV light, a photoinitiator or UV initiator maybegin the polymerization reaction, causing a cured shell to form on thesurface of the deposited layer, while the core remains uncured. Throughthe UV curing of the shell, each newly deposited layer may firmly adhereto the previous layer, preserving layer dimensions and form.

Because photopolymerization is an exothermic process, it may induce asequential process of thermal initiation, which may prolong thepolymerization time (the polymerization stress relaxation period).Prolonging this period may reduce or eliminate deformations and may makethe volume shrinkage more uniform and controllable. As a result, alayer-by-layer structure may be formed with high adhesion between thelayers, reduced anisotropy, and, consequently, enhanced mechanicalperformance. Thus, this dual-cure technique may solve the most importantissues occurring during 3D-printing by photopolymerization.

Dual-curing allows working at low UV-light power, sufficient to form athin shell of the cured polymer to preserve the integrity of the appliedlayer and to control the launching of thermal initiation. Thermalpolymerization is implemented by selection initiator-activator ratio,allowing for reduction of the reaction starting temperature andpromoting of monomer polymerization under conditions occurred as aresult of the layer shell photopolymerization.

The use of dual-curing gives successful results as a stress-reducingapproach. Polymerization stress magnitude is highly dependent on thecomposite's viscous component. The longer it takes for the composite todevelop a high elastic modulus, the more time is available for polymericchains to deform and slip into new positions to adjust to the shrinkage(internal flow), reducing or delaying contraction stress build-up. Theuse of consistent photo- and thermal-polymerization to composeacrylate-based constructive composite promotes an increase in the degreeof conversion, flexural and tensile strength/modulus while significantlyreduces polymerization stress. The prolonged thermal curing reaction ofthe acrylate matrix results in delayed gelation and vitrification,which, in turn, allows for stiffness development in the material to bedelayed to higher conversion which led to significant polymerizationstress relaxation and uniform volume shrinkage. This leads to a decreasein deformations (cracks, delaminations, distortion of the geometry ofthe figure) occurring during the printing process and as a result of thecooling of 3D printed samples, and also allows large-scale printing athigh speeds due to an increase in the deposition rate (10-250 mm/s) andthickness (1-10 mm).

The polymerization reaction of the monomer is accompanied by the releaseof heat and determines the heat balance realized during the curingprocess. There is a temperature threshold upon which the autocatalyticreaction is induced, and the polymerization process becomesuncontrollable and leads to a high polymerization rate and a rapidaccumulation of stresses, which cause the formation of cracks in thesample. Because of the low thermal conductivity of the composite resinpremix and resulting composite material, the temperature control cannotbe provided by external cooling performed using cooling equipment. Inthis case, there may be a temperature gradient (cold surface to hot bulkvolume) that may cause undesirable effects related internal stress,strain and cracks.

To avoid an autocatalytic reaction, the temperature of the printedlayers should be below the temperature threshold which can be achievedby a combination of the matrix and the fillers. The inorganic additivesare characterized by a certain set of thermophysical properties(decomposition temperature, heat capacity, thermal conductivity), whichallow for keeping the maximum temperature of the material below theautocatalytic threshold during printing.

Within photopolymerization, the main source for light scattering throughthe depth of the composite is the interface between the organic andinorganic phases. Moreover, the greater the mismatch between therefractive indices of the cured polymer and inorganic filler, the morelight scattering takes place the lesser the penetration through thedepth of material. Thus, the optical properties of the matrix and one ofthe fillers should coincide in order to provide the formation of thecured shell within photopolymerization with the thickness sufficient tohold deposited layer stable.

In case of dual-curing the high adhesion strength between two layersdetermined by the diffusion of the monomer through the layer border andthe lasting time within which the uncured layer is in contact with thesurface of the previously deposited layer. Improved layers adhesionultimately reduces the anisotropy of the properties of the 3D-printedobjects and enhances mechanical properties, which allow reducingmaterial consumption for the printing of the load bearing constructions.

Dual-cure is a technique, which includes initial illumination withlow-intensity UV light followed by thermal initiation allowing to solvethe most important issues occurring during 3D-printing byphotopolymerization.

TABLE 1 Components of Dual-Cure Composite for 3D Printing ComponentsQuantity Ranges Organic Matrix 10.0 to 30.0 w % Inorganic Hydrate 5.0 to30.0 w % Reinforcing Filler 50.0 to 80.0 w % UV Initiator 0.001 to 0.2 w% Thermal Initiator 0.001 to 0.05 w % Co-initiator 0.001 to 0.05 w %Dye/pigment 0.001 to 0.05 w %

Referencing Table 1, a formulation for a composite material to be usedin dual-cure 3D printing may include an organic matrix comprising atleast one of an acrylate monomer and an acrylate oligomer. Theformulation may further comprise an inorganic hydrate, a reinforcingfiller, a UV initiator, and a combination of thermal initiator andco-initiator (activator). In an embodiment of the formulation, theorganic matrix may be found ranging between about 10.0 to 30.0 w % ofthe formulation. The inorganic hydrate may be found ranging betweenabout 5.0 to 30.0 w % of the formulation. The reinforcing fillers may befound ranging between about 50.0 to 80.0 w % of the formulation. The UVinitiator may be found ranging between about 0.001 to 0.2 w % of theformulation. The thermal initiator in conjunction with the co-initiatorin various ratios may be found ranging between about 0.002 to 0.1 w % ofthe formulation (the summation of each component being found rangingbetween about 0.011 to 0.05 w %).

In some configurations, the organic matrix (acrylate monomer and/oracrylate oligomer) may be Triethylene glycol dimethylacrylate (TEGDMA).Some properties of TEGDMA are found in Table 2.

TABLE 2 Triethylene Glycol Dimethacrylate (TEGDMA) Parameter ValueChemical formula CH₂═C(CH₃)COO(CH₂CH₂O)₃COC(CH₃)═CH₂ Density 1.092 g/mLRefractive index 1.46-1.508 State of Matter Liquid Color Transparent

TEGDMA is a hydrophilic, low viscosity, difunctional methacrylic monomeremployed as a crosslinking agent. TEGDMA is a transparent liquid thatmay found ranging between about 10 to 30 w % of the formulation. Anexemplary matrix may include different polymeric materials. In oneembodiment, the polymeric material may include one or more acrylicoligomers. An exemplary matrix material may be pre-polymerized in orderto enhance the viscosity of the composite.

In some configurations, the organic matrix may be TrimethylolpropaneTrimethacrylate (TMPTMA). Some properties of TMPTMA are found in Table3.

TABLE 2 Trimethylolpropane Trimethacrylate (TMPTMA) Parameter ValueChemical formula [H₂C═C(CH₃)CO₂CH₂]₃CC₂H₅ Density 1.06 g/mL Refractiveindex 1.472 State of Matter Liquid Color Yellow

TMPTMA is a hydrophilic, low viscosity, reactive trifunctionalmethacrylate suitable for use in a wide-ranging number of polymer crosslinking functions. TMPTMA is a transparent liquid that may found rangingbetween about 10 to 30 w % of the formulation.

In some configurations, the organic matrix may be Poly(ethylene glycol)dimethacrylate (PEGDMA). Some properties of PEGDMA are found in Table 4.

TABLE 4 Poly(ethylene glycol) dimethacrylate (PEGDMA) Parameter ValueChemical formula C₃H₅C(O)(OCH₂CH₂)_(n)OC(O)C₃H₅ Density 1.099 g/mLRefractive index 1.464-1.468 State of Matter Liquid Color Transparent

PEGDMA is a long-chain hydrophilic, crosslinking monomer. PEGDMA is atransparent liquid that may found ranging between about 10 to 30 w % ofthe formulation.

In some configurations, a combination of inorganic fillers comprising atleast one reinforcing filler and inorganic hydrate may be used. Theinorganic hydrate may be an inorganic mineral possessing the initialdehydration temperature range needed to keep the composite temperaturebelow the autocatalytic threshold during printing and a refractive indexconforming the refractive index of the cured organic matrix. In thedisclosed formulation, temperature control is achieved by a combinationof the matrix and the fillers. The inorganic additives (inorganichydrates) are characterized by a certain set of thermophysicalproperties (decomposition temperature, heat capacity, thermalconductivity), which maintain the maximum temperature of the materialbelow the autocatalytic threshold temperature during printing.

In some configurations, the inorganic hydrate may be borax decahydrate.Some properties of borax decahydrate may be found in Table 5.

TABLE 5 Borax Decahydrate Parameter Value Chemi|cal formulaNa₂B₄O₇•10H₂O State of Matter Solid Powder Volume weight 0.85 g/cm³Initial decomposition temperature 60-70° C. Refractive index 1.46-1.47Foreign impurities No impurities Particle size distribution D (10) 110 ±20 μm D (50) 310 ± 40 μm D (90) 700 ± 120 μm D max 2800 ± 300 μmSolubility in organic matrix Insoluble

Borax decahydrate is a solid white powder that may be provided in largebags for industrial use. Borax decahydrate may be found ranging betweenabout 5.0 to 30.0 w % of the formulation when combined with thereinforcing fillers but is not limited thereto.

In some configurations, the reinforcing filler comprises at leastaluminum oxide trihydrate or an aluminum oxide trihydrate mixture withat least one of calcium carbonate, talc, silica, wollastonite, calciumsulfate fibers, mica, glass beads, glass fibers, or a combinationthereof. Some properties of the aluminum oxide trihydrate that may beshared with the aluminum oxide trihydrate mixture may be found in Table6.

TABLE 6 Aluminum Oxide Trihydrate Parameter Value Chemical formulaAl(OH)₃ State of Matter Solid Powder Volume weight 0.7 g/cm³ Refractiveindex 1.56-1.58 Foreign impurities No impurities Particle sizedistribution D (10) 5 ± 1 μm D (50) 25 ± 5 μm D (90) 85 ± 15 μm D max200 ± 50 μm Solubility in organic matrix Insoluble

Aluminum oxide trihydrate is a solid white powder that may be providedin large bags for industrial use. Aluminum oxide trihydrate may be usedas a flame retardant and reinforcing filler for the polymer matrix.

In some configurations, the UV initiator may be bisacylphosphine oxides(BAPO)s. Some properties of the BAPO may be found in Table 7.

TABLE 7 Bisacylphosphine oxides (BAPO) Parameter Value Chemical formulaPhenylbis(2,4,6-trimethylbenzoyl)phosphine oxide State of Matter SolidPowder Color Yellowish Solubility in High solubility organic matrix

The UV initiator may induce the polymerization of the organic matrixunder UV-light of a specified wavelength.

In some configurations, the thermal initiator may be benzoyl peroxide(BPO). Some properties of BPO may be found in Table 8.

TABLE 8 Benzoyl peroxide (BPO) Parameter Value Chemical formula C₁₄H₁₀O₄State of Matter Solid Powder Color White Solubility hi TEGDMA 15 w %,23° C.

The thermal initiation may be launched by decomposition of the BPOcatalyzed by the amine activator.

The co-initiator may be bisomer PTE. Some properties of co-initiator aregiven in Table 9.

TABLE 9 Bisomer PTE Parameter Value Chemical formulaN,N-BIS-(2-HYDROXYETHYL)-PARA- TOLUIDINE State of Matter Liquid ColorDark Orange Solubility in TEGDMA High Solubility

In some configurations, the co-initiator may be added into a formulationin advance or may be dissolved in a suitable organic solvent separatelyfrom the composition mixture and added into a formulation right beforeextrusion.

In some configurations, a dye may be found ranging between about 0.01 to0.05 w % of the formulation.

The three-dimensional object is formed from the composite resin premixcontaining components described above by additive manufacturing process,typically layer-by-layer extrusion additive manufacturing. Theformulation may be created following the method disclosed herein. Aresin premix may be generated by blending the acrylate monomers and/oracrylate oligomers, the UV initiator, the thermal co-initiator, and thefillers through operation of the blender for a between about 5 and 20minutes. The photopolymer composite resin may then by created byblending the thermal initiator and the resin premix for a second amountof time. Methods of generating the formulation are described in furtherdetail with regard to FIG. 3 and FIG. 4 .

The 3D printed composite material may be formed by any suitable method.An exemplary method includes layer-by-layer deposition of the compositeresin premix followed by light irradiation. An exemplary light radiationmay be obtained using UV-light or near-UV visible light source. Thelight intensity must be high enough to ensure sufficient curing of theresin at the surface. Because of the solid surface, the extruded layerkeeps its shape and allows the following layers to be extruded on top ofit. At the same time, the polymerization front is being formed, whichpropagates from the surface to the bulk volume of the extruded layer.Simultaneously with light irradiation, or in a short time after theextruded layer was exposed to the light, the thermal polymerizationreaction develops and ensures curing of the whole internal volume of theextruded layer. A 3D printing system capable of creating a 3D printedcomposite material as disclosed herein is described in further detailwith regard to FIG. 4 and FIG. 6 .

FIG. 1 shows an exemplary end material 100 that may be produced via 3Dprinting. The end material 100 is shown as including a matrix material102. The matrix material 102 may be formed via 3D printing.

Exemplary matrix material 102 may include a polymeric material. In oneembodiment, the polymeric material may include one or more acrylicpolymers. An exemplary acrylic polymer may include any polymer that is aproduct of polymerization of an acrylic acid, an acrylate (or ester ofan acrylic acid), and/or a derivative thereof.

The end material 100 may be formed by any suitable methods. An exemplarymethod may include polymerization. Exemplary polymerization may includephotopolymerization, such as radical photopolymerization. In oneembodiment, the end material 100 may be formed by a 3D printing processthat is based on photopolymerization. Exemplary 3D printing processesmay include stereolithography (or SLA, SL, optical fabrication,photo-solidification, resin printing), binder jetting, directed energydeposition, material jetting, powder bed fusion, sheet lamination, vatphotopolymerization, or a combination thereof.

Referencing FIG. 2 , the end material 200 is shown as including at leastone additive each being embedded and/or mixed within the matrix material202 at a selected concentration, respectively. Each additive may includeparticles and/or compounds that possess one or more selected properties.Advantageously, the properties of the additive may be imparted to theend material 200. As illustratively shown in FIG. 2 , the additive inone embodiment may include a first additive 204 and a second additive206. Each of the first additive 204 and second additive 206 may providea respective function to the end material 200.

In one embodiment, the additive may include a reinforcing additive. Thereinforcing additive may improve mechanical properties of the endmaterial 200. For example, the reinforcement additive may increasetensile, flexural, and compressive strength of the end material 200and/or decrease shrinkage of the end material 200 before and after 3Dprinting. Exemplary reinforcing additive may include calcium carbonate,talc, silica, wollastonite, clay, calcium sulfate fibers, mica, glassbeads, glass fibers, or a combination thereof. The reinforcing additivemay be mixed in the end material 200 in the form of particles. Thereinforcing additive particles may be in the form of round and freeformgranules, microcrystals of various shapes, fibers, threads, or acombination thereof. The reinforcing additive may be embedded in the endmaterial 200 at any suitable concentrations. For example, masspercentage (or weight percentage) of the reinforcing additive in the endmaterial 200 may range between about 5 to 80 w % of the end material200.

Additionally and/or alternatively, the at least one additive may includea flame-retardant additive. In one embodiment, the flame-retardantadditive may be mineral-based and/or mineral-occurred. Stated somewhatdifferently, the flame-retardant additive may be of a natural origin.For example, the flame-retardant additive may be derived from a mineral.Exemplary flame-retardant additives may include aluminum oxidetrihydrate, sodium tetraborate decahydrate, boric acid, sodiumphosphate, ammonium sulfate, sodium tetraborate, aluminum hydroxide, ora combination thereof. In contrast to common halogen-based flameretardants, use of the mineral-based flame-retardant additive mayeliminate the presence of toxic substances in combustion products andadvantageously be environmentally beneficial.

Additionally and/or alternatively, the mineral-based flame-retardantadditive may be more resistant to blooming than non-mineral-based flameretardants, including phosphoric acid esters, aluminum polyphosphate,red phosphorus, and other halogen-free flame retardants. Advantageously,the functional stability of the end material 200 does not degrade withthe passage of time. The flame-retardant additive may be embedded in theend material 200 in the form of particles. The reinforcing additiveparticles may be in the form of round and freeform granules,microcrystals of various shapes, or a combination thereof. Theflame-retardant additive may be mixed in the end material 200 at anysuitable concentrations. For example, mass percentage of theflame-retardant additive in the end material 200 may range between about35 to 75 w %, or from about 45 to 65 w % of the end material 200.

Additionally and/or alternatively, the at least one additive may includea coloring agent for coloring the end material 200. Exemplary coloringagents may include a pigment, a dye, or a combination thereof.Additionally and/or alternatively, the at least one additive may includea glittering agent for providing a glittering effect to the appearanceof the end material 200. Additionally and/or alternatively, the at leastone additive may include an aromatic agent for generating an aromaticsmell from the end material 200. Advantageously, the end material 200may have a monolithic amorphous structure with low porosity. The endmaterial 200 may be stronger and lighter than concrete and brick, andresistant to moisture and chemicals. Exemplary end material 200 may bemade by curing non-toxic acrylic-based oligomers and a minimal quantityof photoinitiator, so the making of end material 200 may be safer forhealth reasons.

Although FIG. 2 shows the end material 200 as including the firstadditive 204 and the second additive 206 for illustrative purposes only,the end material 200 may include no additives, or may include any numberof uniform and/or different additives, without limitation. Use of thesame matrix material 202 with various combinations of the additives inthe end material 200 allows obtaining the end material 200 for a widerange of applications.

Referencing FIG. 3 , a method 300 of generating a formulation of aphotopolymer composite material for use in a 3D printing system involvescombining at least one of an acrylate monomer and acrylate oligomerranging between about 10.0 to 30.0 w % of the formulation in a blender,along with an ultraviolet (UV) initiator ranging between about 0.001 to0.2 w % of the formulation, a co-initiator ranging between about 0.001to 0.05 w % of the formulation, a reinforcing filler ranging betweenabout 50.0 to 80.0 w % of the formulation, and an inorganic hydrateranging between about 5.0 to 30.0 w % of the formulation (block 302). Inblock 304, the method 300 generates a resin premix by blending theacrylate monomer/acrylate oligomer, the UV initiator, the co-initiator,the reinforcing filler, and the inorganic hydrate through operation ofthe blender for a first amount of time ranging between about 5 and 20minutes±0.5 minutes.

In block 306, the method 300 combines the resin premix with a thermalinitiator ranging between about 0.001 to 0.05 w % of the formulation inthe blender. In block 308, the method 300 generates a photopolymercomposite resin by blending the thermal initiator and the resin premixthrough operation of the blender for a second amount of time rangingbetween about 5 seconds and 5 minutes.

In some configurations, the method 300 loads the photopolymer compositeresin from the blender into a mixing tank of a 3D printing system (block310). In some instances, in an operation after block 304 and beforeloading the thermal initiator, the mixing tank may not be available, andthe method 300 loads the photopolymer composite resin from the blenderinto a second drum for storage (block 312). In this scenario, block 312returns to block 306 for the addition of the thermal initiator. In someembodiments, this method may be performed because the combination of theresin premix and the thermal initiator cannot be stored together forlonger than about 1 hour. In other embodiments, the photopolymercomposite resin without the thermal initiator, stored in the seconddrum, may be mixed with a mixer after a time interval ranging betweenabout 3 hours to 7 days±0.2 hours before it is transferred from thesecond drum into a mixing tank of a 3D printing system.

FIG. 4 illustrates an embodiment of a mixing system and feeding system400 for generating the photopolymer composite resin for use in a 3Dprinting system. The mixing system and feeding system 400 comprise adrum 402, a barrel pump 404, a flow meter 406, a ribbon blender 408, adischarge valve 410, a pump 412, a hose 414, and a mixing tank 416 of a3D printing system 418.

A drum 402 comprising the organic matrix 424 may be moved to thelocation of the barrel pump 404. The organic matrix 424 may comprise atleast one of an acrylate monomer and an acrylate oligomer. The lid ofthe drum 402 may be cleaned to remove any dust. A special tool may beplaced on the lid of the drum to remove the barrel cap (the larger ofthe two on the drum's lid). The level of organic matrix 424 inside thedrum may be measured and at between about 1-3″ from the top. A barrelpump 404 may be installed into the cap hole of the barrel in a verticalposition. The barrel pump 404 may be placed in fluid communication withan empty ribbon blender 408. The blender's discharge valve 410 may be inthe “closed” position. The barrel pump 404 may be activated, and theflow rate of the organic matrix 424 into the ribbon blender 408 may bemonitored through a flow meter 406. The barrel pump 404 may be turnedoff as soon as the required volume of the organic matrix 424 has beentransferred to the ribbon blender 408, such that the organic matrix 424may be found ranging between about 10.0 to 30.0 w % of the formulation.If the drum 402 is emptied during the pumping procedure, the barrel pump404 may be turned off and reinstalled onto the next drum to continuepumping.

After the organic matrix 424 is added to the ribbon blender 408, thepowdered components 426 may be added into the ribbon blender. Thepowdered components 426 may comprise the UV initiator 432, the inorganichydrate 428, and the reinforcing filler 430.

The UV initiator 432 may be added to the organic matrix 424 within theribbon blender 408 ranging between about 0.001 to 0.2 w % of theformulation. The empty container of the UV initiator 432 may be weighedto ensure that the desired amount of UV initiator 432 has been added tothe ribbon blender 408. If some amount of UV initiator 432 has not beenloaded into the ribbon blender 408, the loading procedure may berepeated. After the UV initiator 432 has been added, the container maybe closed to protect the powder from sunlight and moisture.

The co-initiator 434 may be added to the organic matrix 424 within theribbon blender 408 ranging between about 0.001 to 0.05 w % of theformulation. The empty container of the co-initiator 434 may be weighedto ensure that the desired amount of co-initiator 434 has been added tothe ribbon blender 408. If some amount of co-initiator 434 has not beenloaded into the ribbon blender 408, the loading procedure may berepeated. In some configurations, the co-initiator may be added into aformulation in advance. In some configurations, the co-initiator may bedissolved in a suitable organic solvent 436 separately from thecomposition mixture and may be added into a formulation right beforeextrusion by the 3D printing system 418.

In some formulations, an acrylate prepolymer may be generated byshort-term irradiation of acrylic monomers/oligomers combined withlimited amount of photoinitiator. This action may increase viscosity ofthe acrylic monomers/oligomers to prevent filler particles fromsedimentation and may allow the reactivity of the resulting prepolymermixture to be adjusted.

The reinforcing filler 430 may be added after the UV initiator 432. Insome instances, the reinforcing filler 430 may come in 55 lb bags. Toensure that the correct amount of the reinforcing filler 430 is added,the bag of the reinforcing filler 430 may be placed on a floor scale andweighted to obtain the total mass of the load. A safety grating may beinstalled within the ribbon blender 408, and the bag of the reinforcingfiller 430 may be opened and loaded into the ribbon blender 408 throughthe safety grating. When the bag is emptied after loading, the empty bagmay be weighed. The mass of reinforcing filler 430 inside the ribbonblender 408 may be calculated by subtracting the weight of the emptiedbag from the total mass weight taken initially. Additional reinforcingfiller 430 may be added to the ribbon blender 408 to meet the quantityrange of about 50.0 to 80.0 w % of the formulation. The ribbon blender408 may then be turned on for about 10 minutes to form a premix resinfrom the components before adding the inorganic hydrate 428.

The inorganic hydrate 428 may be added after the reinforcing filler 430.In some instances, the inorganic hydrate 428 may come in 55 lb bags. Toensure that the correct amount of the inorganic hydrate 428 is added,the bag of the inorganic hydrate 428 may be placed on a floor scale andweighted to obtain the total mass of the load. A safety grating may beinstalled within the ribbon blender 408, and the bag of the inorganichydrate 428 may be opened and loaded into the ribbon blender 408 throughthe safety grating. When the bag is emptied after loading, the empty bagmay be weighed. The mass of inorganic hydrate 428 inside the ribbonblender 408 may be calculated by subtracting the weight of the emptiedbag from the total mass weight taken initially. Additional inorganichydrate 428 may added to the ribbon blender 408 to meet the quantityrange of about 5.0 to 30.0 w % of the formulation. The ribbon blender408 may then be run for 12 hours in order to mix the components.

In some formulations, the resin premix may be generated by blending theorganic matrix 424, the UV initiator 432, the thermal co-initiator 434,and the fillers through operation of the ribbon blender 408 for a firstamount of time ranging between 5 minutes and 20 minutes, followed byblending with the thermal initiator 438 in liquid form for a secondamount of time ranging between 5 seconds and 60 seconds. The thermalinitiator 438 may be at least partially dissolved in acrylate monomer toform the liquid thermal initiator.

In some formulations, the resin premix may be generated by blending theorganic matrix 424, the UV initiator 432, the thermal co-initiator 434,and the fillers through operation of the ribbon blender 408 for a firstamount of time ranging between about 5 and 20 minutes, followed byblending with the thermal initiator 438 in powder form for a secondamount of time ranging between 30 seconds and 5 minutes. The thermalinitiator 438 may be added such that it may be found in the quantityrange of about 0.001 to 0.05 w % of the formulation.

The pump 412 may be positioned underneath a discharge valve 410 of theribbon blender 408. In an embodiment, the pump 412 may be connected tothe mixing tank 416 of a large gantry 3D printing system 418 through theuse of a hose 414. Any appropriate 3D printing system may be used, andthe disclosure is not limited to the large gantry 3D system. The gantrysystem (GS) mixing tank 416 may be inspected to ensure that it isoperational and ready to receive the mixed components as a resin. Thepump may be turned on before the discharge valve 410 is moved into the“open” position. The GS mixing tank 416 may be inspected to ensure thatthe photopolymer composite resin is being collected. When the flow rateof resin from the ribbon blender 408 starts to decrease, the ribbonblender 408 may be turned on to push the remnants of the resin into thepump's hopper. The pumping procedure may end when the ribbon blender 408is emptied, at which point the ribbon blender 408 and the pump may beturned off.

In some embodiments, the resin premix generated by blending the organicmatrix 424, the UV initiator 432, the thermal co-initiator 434, and thefillers through operation of the ribbon blender 408 for a first amountof time ranging between about 5 and 20 minutes may be blended with thethermal initiator 438 for a second amount of time directly in theextruder of the 3D printing system 418, before the resin premix isdeposited and cured.

In some instances, the GS mixing tank 416 may be unavailable to receivethe photopolymer composite resin, and the resin may be loaded into astorage drum 420. The hose 414 from the pump 412 may be positioned andsecured within the storage drum 420 instead of the GS mixing tank 416.The pump may be turned on before the discharge valve 410 is moved intothe “open” position. When the flow rate of resin from the ribbon blender408 starts to decrease, the ribbon blender 408 may be turned on to pushthe remnants of the resin into the pump's hopper. The photopolymercomposite resin from the ribbon blender 408 may be pumped into one ormore drums, based on the total volume of the resin within the ribbonblender 408. If a pump 412 cannot be used, an empty drum may be placedbeneath the discharge valve 410, and the discharge valve 410 may beopened to pour the photopolymer composite resin into the drum. Thedischarge valve 410 may be closed as soon as the drum is full.

In some embodiments, the resin premix generated by blending the organicmatrix 424, the UV initiator 432, the thermal co-initiator 434, and thefillers through operation of the blender for a first amount of timeranging between about 5 and 20 minutes may be stored for a period oftime up to 12 months before being blended with the thermal initiator 438for a second amount of time.

Before printing with the photopolymer composite resin stored in astorage drum 420, the resin may require mixing. A mixer 422 such as amanual mixer may be utilized to mix the resin before transferring theresin to a GS mixing tank 416. The lid of the storage drum 420 may beopened and the paddle of the mixer 422 may be positioned into the drumbetween the center of the drum and the inner wall. The upper layer ofthe resin may be mixed by moving the paddle clockwise with the mixer onuntil the upper layer of the drum becomes homogenous. The paddle maythen be pushed to the bottom of the drum. The bottom layer may then bemixed by moving the paddle outward from the center, then up toward theupper layer of the resin near the inner wall of drum, then pushed backdown toward the bottom of the drum while being moved in a counterclockwise rotation around the center of the drum. Mixing may continueuntil the resin is homogenous.

To prevent the contamination of the inner surface of the ribbon blender408 with dye/pigment 440, which may influence the production ofuncolored resin, the coloring procedure may be carried out onphotopolymer composite resin in storage drums, which may then be labeledin accordance with the color of the dye/pigment 440 used. The necessaryamount of dye/pigment 440 may be weighed out and placed into a layer ofresin within the drum. A manual mixer may be utilized to mix thedye/pigment 440 with the photopolymer composite resin. After thedye/pigment 440 has been added, the resin in the drum may be mixed againafter about 24 hours of storage before it is ready to be transferred tothe GS mixing tank for use in 3D printing.

After about 12 hours of continuous mixing, the photopolymer compositeresin may be considered to be ready for use. The photopolymer compositeresin may require handling while in storage. As resin is pumped into theGS mixing tank, it may be mixed continuously until it is all consumed.Up to about 3 hours without mixing may be acceptable. In cases where theresin is kept in drums for long-term storage, the following criteria mayneed to be met:

-   -   Keep drums sealed at all times    -   Avoid exposing resin to light and moisture    -   Keep foreign impurities out of drums    -   Manually mix resin once every seven days    -   Do not attempt to print with resin that has gone unmixed for        more than three hours

In some instances, the resin may undergo a quality assurance process.After the resin has been mixed for about 12 continuous hours, a 500 mLbatch may be taken for testing. Three samples may be obtained whilepumping a batch out from the ribbon blender. All samples may be takenfrom the hose end to the GS mixing tank or the second drum.

A first sample of about 150 to 200 mL may be taken 10 to 15 secondsafter pumping begins. A second sample of about 150 to 200 mL may betaken in the middle of the pumping procedure. A third sample of about150 to 200 mL may be taken 10 to 15 seconds before pumping stops.

For resin in drum storage, the sampling procedure may be as follows:

-   -   A first sample of about 150 to 200 mL may be taken from the        first drum    -   A second sample of about 150 to 200 mL may be taken from the        second drum    -   A third sample of about 150 to 200 mL may be taken from the        third drum

Storage in this embodiment may use three different drums, since a singleload of the mixer may be equal to three drums in volume. About 100 mLfrom each sample may be put into a glass or PE container, mixed well,and sealed for quality assurance procedures.

FIG. 5 illustrates a method 500 in accordance with one embodiment. Inblock 502, a resin premix material is provided. The resin premix maycomprise at least one of acrylate monomer and acrylateoligomer˜10.0-30.0 w % of formulation 512, which in some embodiments maybe Triethylene glycol dimethylacrylate (TEGDMA) 524. The resin premixmay further comprise inorganic hydrate˜5.0-30.0 w % of formulation 514,which in some embodiments may be borax decahydrate 526. The resin premixmay further comprise reinforcing filler˜50.0-80.0 w % of formulation516, which in some embodiments may be aluminum oxide trihydrate oraluminum oxide trihydrate mixture 528. The resin premix may furthercomprise ultraviolet (UV) initiator˜0.001-0.2 w % of formulation 518,which in some embodiments may be bisacylphosphine oxides (BAPOs) 530.Finally, the resin premix may comprise co-initiator˜0.001-0.05 w % ofphotopolymer composite resin 520, which in some embodiments may bebisomer PTE 532.

In block 504, the resin premix provided in block 502 is mixed withthermal initiator˜0.001-0.05 w % of photopolymer composite resin 522,which in some embodiments may be benzoyl peroxide 534 to form aphotopolymer composite resin.

In block 506, the photopolymer composite resin is extruded by a 3Dprinter into a layer. The first layer rests upon a support. Subsequentlayers are extruded onto previous layers, to build up a materiallayer-by-layer. In block 508, the layer just extruded is at leastpartially cured using light irradiation. This curing irradiation may beprovided by a UV curing module. If the final photopolymer compositematerial desired is not yet complete, decision block 510 goes back torepeat block 506 and block 508 until the material is complete. Once thefinal desired material has been built, the method 500 is complete.

Referencing FIG. 6 , a printing system 600 comprises a material feedingsystem 602, a printing head 620, and a control system 632. The materialfeeding system 602 comprises an input from a material storage tank 604,a material feed hopper 606, pumps for feeding material from the hopper(dosing pump 612 and/or at least one feeding pump 608), and supply hoses610 with auxiliary equipment (auxiliary equipment 614, auxiliaryequipment 616, and auxiliary equipment 618) to assist the movement ofthe material to the printing head 620. The printing head systemcomprises a connector 622, an extruder 624, a nozzle 626, and a curingmodule 628, which may include at least one light curing module 630.

The material feeding system 602 may be substantially similar in whole orpart to the mixing system and feeding system 400 illustrated in FIG. 4 .The control system 632 may be operatively connected to the curing module628 allowing the control system 632 to control operation of the curingmodule 628. In some configurations, the printing head includes an activefeedback system 636 for monitoring material curing and communicatinginformation to the control system 632.

In some configurations, the control system 632 may include controlsystems that control the curing module, such as the curing modulecontrol system 634. In this configuration, the curing module controlsystem 634 may control, for example, the activation of LEDs in thecuring module and their output intensity. The separation of the systemsmay facilitate maintenance and allow for the exchange or substitution ofthe modules for different printing jobs. For instance, the curing modulemay be replaced with its corresponding control system instead for acuring module and control system with different operational parametersbetter suited for the particular printing job. In this configuration,the active feedback system 636 may communicate information to the curingmodule control system 634. The control system 632 may be substantiallysimilar to the embodiment illustrated in FIG. 7 .

Referencing FIG. 7 , the control system 700 comprises an automaticcontroller 728 communicating with a control panel 726, a motioncontroller 732 communicating with motor drivers 708, and input/outputmodules 730 communicating with limit switches 702, an auxiliaryequipment connection 704, and a frequency converter 706. The motordrivers 708 communicate with Z axis motors 710, X axis motors 712, and Yaxis motors 714, for positioning the printing head within the printingarea. The motor drivers 708 additionally control C axis motors 716 thatcontrol the position of the curing module of the printing head withrespect to the extruder and nozzle. The control system 700 alsocommunicates with an operator monitor 720 and a safety controller 722that communicates with safety sensors 724.

The control system 700 additionally communicates with curing module 718,controlling operation of the curing module 718 for irradiating thepoured resin for curing.

The control system 700 may include an electronics unit with software formanual and automatic modes of operation. The control system 700 may beoperated to monitor and control operations of controlled systems such asthe positioning system, material feeding system, printing head system,and auxiliary equipment (such as CNC milling/smoothing system). Thecontrol of the positioning system may be based upon the principles ofComputer Numerical Control (CNC). Control of the material feeding systemand printing head system may be based on the principles of automaticcontrol and may utilize software algorithms to provide real-timemonitoring and control of the processes. The auxiliary equipmentcontrols may include safe operation sensors, emergency sensors andadditional safety systems and equipment.

Human monitoring and control systems may provide function monitoring andmanual control operation by the 3D printer operator. Communicationinterfaces provide data communication between the different devices andare also used for G-code program loading to the control system.

The positioning system may include a rigid frame assembled from anindustrial grade aluminum profile rigidly fixed inside the freightcontainer or other suitable positioning systems, such as a portal-basedsystem. The build platform is represented by the inner floor surface ofthe freight container. The 4-axis linear motion system may includelinear guides, stepper motors with reduction gears, ball-screw pairs, abelt drive, and end position sensors.

In an exemplary material extrusion process, a printing material is fedby a material-feeding system through the deposition nozzle. The nozzletraverses via a positioning system to build up an object while a curingmodule 718 cures the viscous material, forming a hard structure layer bylayer. The curing module 718 may be an Ultraviolet (UV) optic system.Operation of the curing module 718 may be configured through the controlsystem 700. The control system 700 may monitor and control variables ofthe printing process that are translated from programming instructionsloaded by a user. Key process variables, which may make up a printprofile, may include material, nozzle diameter, print speed (a combinedparameter made up of the feed rate of the material and the movementspeed of the positioning system), curing module 718 power usage, curingmodule intensity, (e.g., light intensity), curing module 718 position,and layer thickness.

The control system may also control operation and movement of theprinting head. The printing head moves along programmed line segments onthe XY plane and extrudes a viscous printing material which is cured byirradiation from the curing module. The cured material hardens andadheres to the previous layer. After executing all of the commands forthe current layer, the printer gantry moves upward by the height of onelayer (ZY and ZX plane) and starts to print the next layer. A designedobject may be formed by repeating this process for all of the layers. Anexample of the programmatic instruction utilized to control the printinghead are found below.

G-Code

Sep. XX, 20XX at 11:40:43 A M

Settings Summary

; processName, top_1

; applyToModels, test_1.O

; profileName, Container

; profileVersion, 20XX-06-XX 11:29:58

; baseProfile, Default

; printMaterial,FS

; printOuality, Fast

; printExtruders,

; extruderName,extruder 1

; extruderDiameter, 20

; layerHeight, 4

; exportFileFormat, gcode

; defaultSpeed, 1800

; rapidXYspeed, 18000

; rapidZspeed, 3000

G90

M82

M106 S255

M104 SO TO

G28; home all axes

G1 Z4.000 F3000

process top_1

Layer 1, Z=4.000

TO

; tool H4.000 W20.400

; external single extrusion

G1 X53.606 Y234.319 F18000

G92 E0

; tool H4.000 W20.823

G1 X57.672 Y233.605 E3.0405 F1800

; tool H4.000 W20.055

G1 X61.738 Y233.551 ES.9250

In some configurations, the printing head may be operatively coupled toa non gantry type printing system to position and orient the printinghead in the formation of the printed component. For instance, theprinting head may be operatively coupled to an articulating arm (e.g.,spider, robotic arm, etc.) that moves and positions the printing headwithin the three-dimensional space of the printing area to form theextruded material layers of the printed component. In thisconfiguration, the programmatic instructions may differ from theprogrammatic instructions utilized in the gantry system to account forthe different range of motion provided by the different system.

In some configurations, the control signal may be communicated to theprinting head through a wired communications method (e.g., ethernet,USB, fiber optic cable, etc.). The wired communications method may becombined with the cables that deliver power to the LEDs and movement ofthe curing module. The wired connection for control signals to thecuring module may be combined in a wiring harness/assembly with thepower cable for the curing module.

In some configurations, the control signal may be communicated to theprinting head through a wireless communications system. The utilizationof the wireless communications system to communicate and receive thecontrol signals between the printing head and the control system mayeliminate the disadvantages associated with hard wiring such as weightreduction and the possibility of wires interfering with the printingprocess, extruded material layer, etc.

The material feeding system may include input from a material storagetank, a material feed hopper, pumps for feeding material from thehopper, and supply hoses with auxiliary equipment that carry thematerial to the printing head system.

The printing head system may include a device for extruding the materialthrough an aperture of a predetermined shape and profile—the depositionnozzle, a mechanism for rotating the nozzle and curing module around theZ axis, and the light curing module, which is the source of ultravioletlight for curing the material.

FIG. 8 illustrates a curing comparison 800 in accordance with oneembodiment. A first 3D printing system 802 may extrude layers ofphotopolymer composite resin containing a photoinitiator onto a support804. The 3D printing system 802 may include a light curing module thatcures each layer substantially or completely through as it is deposited.The layers from photo-curing only 806 may exhibit distortions such ascracks, deformation 814, and delamination 816, related to the quickcuring needed to completely cure the layer through, as shown.

In contrast, a 3D printing system 808 may deposit layers of photopolymercomposite resin containing a photoinitiator, a thermal initiator, and aco-initiator onto a support 810. UV light from the 3D printing system808 curing module may briefly cure an outer shell of the deposited resinin order to adhere the layers and create the layer structure. Theremaining core of uncured resin may slowly cure from thermal energygenerated as a byproduct of photo curing and/or from heat applied aspart of a further curing process. The resulting dual-cured layers 812are better able to maintain adherence and their desired shape once fullycured due to the dual-curing process. This is shown in further detail inFIG. 9 .

FIG. 9 illustrates a curing process detail 900 in accordance with oneembodiment. The curing process detail 900 illustrates uncured materialjust extruded 902, UV curing light 904, UV cured shell 906, uncured core908, layer adhesion 910, curing heat 914, and fully dual-cured material916.

An extruder of a 3D printer may deposit uncured material just extruded902 onto either a support, in the case of the first layer, or onto aprevious layer. The curing module of the 3D printer may emit a UV curinglight 904. This UV curing light 904 may be calibrated to work inconjunction with a UV initiator within the uncured material justextruded 902 in order to create a UV cured shell 906 from the outermostportion of the uncured material just extruded 902. The adhesion of theuncured material just extruded 902 with the UV cured shell 906 of thepreviously extruded layer may allow a strong layer adhesion 910 betweeneach subsequent layer and the layer preceding it. The UV cured shell 906may also allow each extruded layer to maintain its shape and structure,in spite of not being fully cured.

Within the UV cured shell 906 of each layer there may remain an uncuredcore 908. This uncured core 908 may be a result of the amount andwavelength of UV light emitted by the curing module. The uncured coremay also result partially or in whole from the inclusion of additiveswithin the resin matrix that scatter or block UV radiation, preventingthe UV curing light 904 from penetrating beyond the outermost region ofextruded material.

The uncured core 908 may be slowly cured by the action of a thermalinitiator within the extruded material. Heat may be applied from anexternal source and/or may be a byproduct of the photo curing process.This heat may act with the thermal initiator to slowly complete thecuring process, even when additives or layer thickness 912 prevent thedeeper penetration of UV light. This dual-cure may result in tightlybonded and structurally sound layers of fully dual-cured material 916with a greater layer thickness 912 (in some cases 10 mm or more) than ispossible with UV curing alone.

FIG. 10 is a photograph of a 3D printed, dual-cured material includingdifferent thicknesses of layers with carbon dust 1000 in accordance withone embodiment. Utilizing a dual-curing photopolymer composite resin,carbon dust may be added and because the final curing stage relies onthermal energy (heat), which the carbon dust does not block, the finaldeposited layers with carbon dust 1002 may be even (if desired), tightlyadhered, and capable of being built up to a considerable thickness, suchas the almost 10 mm seen in the illustrated example.

In a configuration not utilizing a dual-curing process, the depositedlayers with carbon dust 1002 may only photo cure through the interactionof UV light with a UV initiator within the photopolymer composite resin.The layers fail to cure completely and evenly, due to the way in whichthe carbon dust may block the scatter the UV light from the light curingmodule. The blocked and scattered light may be unable to penetratedeeply enough into the layer to provide a full cure.

FIG. 11 illustrates cellular structure concepts 1100 comprising astructural wall 1102, hollowed out portions 1104, and an in-fill pattern1108, while the structural wall 1106 comprises just the in-fill pattern1108. A wall structure with a special infill pattern may be utilized toincrease material load bearing capacity without using additionalreinforcement. The structural layers are printed using a cellularstructure for better tensile strength and integrity. The 3D printingmethod utilizing dual-cure photopolymer composite materials disclosedherein, allows the building of structural elements with differentgeometries which are much better able to sustain loads compared to manymaterials commonly used in construction today.

EXAMPLES

The total structure of 3D printed parts may have some anisotropy ofmechanical properties, because of layer-by-layer deposition. The effectof anisotropy may manifest itself in the percent difference in theproperties of the printed parts along and across the deposited layers.However, a dual-curing system of initiators may reduce overallanisotropy of the printed parts. A comparative example showing theresulting products from the composition with and without the thermalinitiator is shown in Table 10.

TABLE 10 Properties of 3D Printed Dual-Cured Composite in comparisonwith the Photopolymerized Composite Dual-cured PhotopolymerizedParameter along across along across Ultimate compressive 71 ± 4 70 ± 7 58 ± 3 66 ± 5  strength, MPa Yield strength, MPa 60 ± 4 52 ± 5  47 ± 752 ± 4  Compressive modulus 8400 ± 800 5400 ± 400  4100 ± 780 4600 ±1300 of elasticity, MPa Relative compressive  2.0 ± 0.8 3.0 ± 1.0  4.3 ±0.6 5.0 ± 1.0 deformation, % Ultimate tensile 10.5 ± 0.7 7.0 ± 1.6  10 ±1.0 5.5 ± 1.2 strength, MPa Tensile modulus of 11000 ± 1870 9400 ± 17005700 ± 680 5900 ± 1700 elasticity, MPa Relative tensile  0.1 ± 0.02 0.08± 0.02  0.2 ± 0.02  0.1 ± 0.03 deformation, %

Photopolymerized Composite may be generated by blending the acrylatemonomers, the UV initiator, and the fillers shown in Table 11 throughoperation of the blender for 20 minutes. Dual-Cure Composite may begenerated by blending the acrylate monomers, the UV initiator, thethermal co-initiator, and the fillers shown in Table 11 throughoperation of the blender for 20 minutes. The thermal initiator may beadded to the premix just before the composite is extruded.

TABLE 11 Components of Composites for 3D Printing System QuantityRanges: Quantity Ranges: Components Dual-Cure PhotopolymerizationOrganic Matrix 23 to 29 w % 23 to 29 w % Inorganic Hydrate 22 to 24 w %22 to 24 w % Functional Filler 50 to 54 w % 50 to 54 w % UV Initiator0.07 to 0.09 w % 0.07 to 0.09 w % Thermal Initiator 0.03 w % 0 w %Co-initiator 0.02 w % 0 w % Dye/pigment 0 w % 0 w %

Extrusion-based 3D printer equipped with a UV LED light source may beused for printing. The LED may be selected with the peak wavelength at417 nm. The maximum light intensity of the UV LED light source on thetop of the deposited layer may be 42 to 43 W/cm² with a diameter of spotsize of about 20 mm. The nozzle passage speed of 40 mm/sec may beapplied with the feeding rate of the composite into the nozzle (internaldiameter of 10 mm) of 2×10³ to 2.5×10³ mm³/sec, which may lead to theformation of the layer with a width of 16 mm and height of 4 mm.Photopolymerized material may be printed by applying 100% of the UV LEDlight source intensity. In case of dual-cure polymerization process, 3to 6% of the maximum intensity of the light source may be used. Theapplied light irradiation may allow control of the initiation of thepolymerization reaction at the surface. The chosen concentration of BAPOand light intensity may limit the penetration depth and allow thereaction to accumulate near the top surface of the deposited layer,thereby supporting the formation of the solid shell and avoidingdeformation of the surface due to rapid solidification and volumeshrinkage. As a result, the solid shell may form with the thickness of0.5 to 1 mm, which may hold the shape of the layer.

Compared to the composite polymerized by applying the dual-curingsystem, the photopolymerized composite may exhibit lower mechanicalperformance. For the dual-cured composite, the difference of 33% may beobserved for the ultimate tensile strength. The ultimate compressivestrength values along and across the printed layers may be equal. Thedecrease in difference between the properties of the printed parts alongand across the deposited layers may be caused by a reduction inanisotropy due to improved layer adhesion for the 3D printed parts. Thephotopolymerized composite may exhibit 14% distinction in the ultimatecompressive strength values and 45% distinction in the ultimate tensilestrength values. Higher stiffness of the dual-cured formulation may bedue to enhancement of the conversion degree of the material withinsequential photo- and thermal-polymerization curing.

The methods and formulations in this disclosure are described in thepreceding on the basis of several preferred embodiments. Differentaspects of different variants are considered to be described incombination with each other such that all combinations that upon readingby a skilled person in the field on the basis of this document may beregarded as being read within the concept of the invention. Thepreferred embodiments do not limit the extent of protection of thisdocument.

Having thus described embodiments of the present invention of thepresent application in detail and by reference to illustrativeembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of the presentinvention.

The invention claimed is:
 1. A method of 3D printing a photopolymer composite material for a building component of a residential or commercial building, the method comprising: accessing a 3D printing system comprising: a control system, a mixing system, including a mixing tank, a feeding system in fluid communication with the mixing system, a light curing module controlled by the control system, and a printing head controlled by the control system, the printing head including: an extruder in fluid communication with the feeding system, and a nozzle in fluid communication with the extruder; a. providing a resin premix material including: i. at least one of an acrylate monomer and an acrylate oligomer in the range between about 10.0-30.0 w % of a photopolymer composite resin; ii. an inorganic hydrate in the range between about 5.0-30.0 w % of the photopolymer composite resin; iii. a reinforcing filler in the range between about 50.0-80.0 w % of the photopolymer composite resin; iv. an ultraviolet (UV) initiator in the range between about 0.001-0.2 w % of the photopolymer composite resin; and v. a co-initiator in the range between about 0.001-0.05 w % of the photopolymer composite resin; b. mixing in the mixing tank a thermal initiator in the range between about 0.001-0.05 w % of the photopolymer composite resin with the resin premix material to form the photopolymer composite resin, wherein the thermal initiator is supplied from the feeding system; c. extruding a layer of the photopolymer composite resin the nozzle onto a support while the support is moving relative to the layer, wherein the nozzle is instructed via the control system to extrude the layer of the photopolymer composite resin onto the support; d. partially curing, via the light curing module, the layer using light irradiation to form an initial layer of photopolymer composite material arranged in a spatial configuration, wherein the partially curing results in curing only an outer shell of the extruded layer using light irradiation; and e. repeating steps c and d for each subsequent layer to create a multi-layered structure of the photopolymer composite material to form a building component or a complete building.
 2. The method of claim 1, wherein the thermal initiator is added directly to the extruder of the 3D printer where the thermal initiator is mixed with the resin premix material before the photopolymer composite resin is extruded.
 3. The method of claim 1, wherein the thermal initiator is a powder and the thermal initiator is mixed with the resin premix material for about 30 seconds to 5 minutes.
 4. The method of claim 1, wherein the thermal initiator is a liquid and the thermal initiator is mixed with the resin premix material for about 5 seconds to 60 seconds.
 5. The method of claim 1, further comprising: a. forming an acrylate prepolymer by: i. blending a portion of the acrylate monomers or the acrylate oligomers with a portion of a UV initiator to form a prepolymer mixture; and ii. irradiating the prepolymer mixture with light to form the acrylate prepolymer, wherein the irradiating only partially polymerizes the prepolymer mixture; and iii. mixing the acrylate prepolymer into the resin premix.
 6. The method of claim 1, wherein partial curing of the layer in step d) and activation of the thermal initiator by the co-initiator induces polymerization and a release of heat, which induces an autocatalytic polymerization reaction at and above an autocatalytic threshold temperature.
 7. The method of claim 6, further comprising replacing the resin premix material with a new resin premix material, wherein an amount of the inorganic hydrate in the new resin premix material is the amount effective to keep a layer temperature below the autocatalytic threshold temperature.
 8. The method of claim 6, wherein each layer in steps c)-e) remains at a temperature that is below the autocatalytic threshold temperature.
 9. The method of claim 1, wherein the co-initiator is bisomer PTE.
 10. The method of claim 1, wherein the resin premix further comprises a dye or pigment in the range between about 0.001-0.05 w % of the photopolymer composite resin.
 11. The method of claim 1, wherein the acrylate oligomer is Triethylene glycol dimethylacrylate (TEGDMA).
 12. The method of claim 1, wherein the layer has a thickness in the range between about 1 mm and 10 mm, and the layer is extruded by a single pass of a printing head of the 3D printer.
 13. The method of claim 1, wherein the reinforcing filler comprises at least aluminum oxide trihydrate or an aluminum oxide trihydrate mixture with at least one of calcium carbonate, talc, silica, wollastonite, calcium sulfate fibers, mica, glass beads, glass fibers, or a combination thereof.
 14. The method of claim 1, wherein the UV initiator is bisacylphosphine oxides (BAPO)s.
 15. The method of claim 1, wherein the thermal initiator is benzoyl peroxide.
 16. The method of claim 1, further comprising using the building component by assembling the building component with other building components for building structure.
 17. The method of claim 1, wherein the building component or the complete building is monolithically integrated.
 18. The method of claim 1, wherein a core of the layer uncured by light irradiation is subsequently cured using thermal energy.
 19. The method of claim 18, wherein a subsequent layer is extruded atop the layer before the core of the layer is subsequently cured by the thermal energy. 